If the cache is out-of-process, access is going to be subject to faults and latencies that are categorically different than anything that would be in-process.

If the cache is out-of-process, access is going to be subject to faults and latencies that are categorically different than anything that would be in-process. You'd never want to include a request to an out-of-process service in any kind of hot loop, even if that service is on the same machine.